The present invention relates generally to systems for depositing a material onto a surface, and more particularly, to spraying devices for spraying coatings onto circuit boards in the conformal coating industry.
Uniform thickness coatings are often applied over sections of circuit boards. The coatings prevent water vapor, gases, or fluids from corroding the electrical connections on a circuit board. The coatings may comprise a wide variety of materials such as ultraviolet (UV) acrylic gels, moisture and thermal cure silicones, and the like.
The coatings are typically applied to a circuit board using devices such as spray guns or spray nozzles. Such devices generally include a liquid spray material that is atomized by compressed air and is then directed toward the surface to be coated. The spraying devices are commonly attached to an apparatus, such as a multi-degree of freedom robotic positioning apparatus, that provides accurate positional displacement relative to the article being coated.
As electronic components mounted on circuit boards become smaller, and more compactly spaced, previous large diameter spray nozzles can no longer access particular areas of a circuit board. Some tall electronic components protrude a considerable distance from the circuit board. When two or more of these tall electronic components are closely spaced, a large diameter spray nozzle cannot fit between the electronic components. Furthermore, there is now a requirement for providing a small diameter spray pattern with clearly defined edges to provide the accuracy and precision required to produce the spray in the narrowly defined space created by the closely spaced electronic components.
In order to overcome the above deficiencies, the present invention provides a compact spray valve that produces a small diameter spray pattern using an extended atomizing air cap. The extended atomizing air cap can reach between tall closely spaced electronic components, and can thereby apply spray to the circuit board between the components. The compact spray valve of the present invention includes an air body, a fluid control body, and an extended atomizing air cap. The extended atomizing air cap has a small outside diameter combined with a long length, allowing the extended atomizing air cap to reach between tall and closely spaced electronic components on a circuit board.
In the air body of the compact spray valve, a piston is attached to a fluid control needle. The fluid control needle protrudes from the air body and enters into the fluid control body where the tip of the fluid control needle is received in a valve seat. Pressurized air is selectively applied to the top or the bottom of the piston causing the piston to move in an upward or downward direction, thereby causing the tip of the fluid control needle to move into or out of the valve seat.
In the fluid control body, material to be applied to a surface is supplied in a fluid form. The material flow is controlled by the location of a tip of the fluid control needle. When pressurized air is applied to the top of the piston in the air body, the fluid control needle is moved in a downward direction until the tip of the fluid control needle is fully seated in the valve seat, thereby stopping the flow of material. When pressurized air is applied to the bottom of the piston in the air body, the tip of the fluid control needle is moved upward out of the valve seat, allowing material to flow through the valve seat into an atomizing space. At the same time, compressed air is supplied to the extended atomizing air cap. The extended atomizing air cap is attached to the lower portion of the fluid control body by a threaded retaining ring. The compressed air flows through the extended atomizing air cap and into the atomizing space causing the fluid stream to be atomized into a spray.
For generating a round spray pattern, a plurality of longitudinal air conduits are formed between a cylindrical outer body of a seat extension and a fluted interior surface of the extended atomizing air cap. The longitudinal air conduits create laminar flow air columns that eject into the atomizing space and atomize the material. The atomized material flows out through a round opening in the atomizing air cap producing a round spray pattern with distinctly defined edges. This round spray pattern is then projected onto a circuit board surface.
For generating a flat spray pattern, an extended flat spray atomizing air cap, hereafter referred to as a xe2x80x9cflat spray air capxe2x80x9d, is attached to the fluid control body. In the flat spray air cap, a plurality of longitudinal air conduits are formed between a cylindrical outer body of a seat extension and a fluted interior surface of the flat spray air cap. The longitudinal air conduits create laminar flow air columns that eject into the atomizing space to atomize the fluid. The flat spray air cap also has side air passages that provide inwardly directed jets of air which cause the atomized spray to form into a flat spray pattern in the atomizing space. This flat spray pattern is then projected onto the circuit board surface.